Thought I would share my experience so far with sixlines.
First off, one of my favorite fish. But, I am actually on my 3rd sixline right now, something I am not too proud to admit.
My first one was great, got along well with my two clownfish. I had a cover for the aquarium, but one day I left slightly ajar due to some maintance;he found his way out a small opening and went carpet surfing. My second sixline was a bit smaller, probably 1.5". After l put him in the tank he headed for the rockwork and was not to be seen again. I do not know what happened with him. I eventually bought a third, and he has been hardy and active just like the first. I have had him probably 6 months now. While apparently they can be territorial, I did add a fourth fish several months later, a pajama cardinal, and the sixline has not been aggressive towards him in the least. Just thought I would share my experience.